1. Field of the Invention
The invention concerns a mechanical supercharger for an internal combustion engine and having a sliding bearing mechanism.
2. Description of Related Art
A conventional mechanical supercharger is shown in Japanese Patent Laid-open No. 62-199928. This conventional mechanical supercharger is shown in FIG. 5. Therein, reference numeral 220 indicates a rotor which is fixed to a rotor shaft 221 by a fastening pin 222, and the both ends of the shaft are rotationally supported in a housing 224 via sliding bearing 223. The housing 224 includes a rotor-housing 225a, a bearing-housing 225b which supports the sliding bearings 223, and two side-housings 226a, 226b which are respectively fixed to the rotor-housing 225a and the bearing-housing 225b.
Two of the rotors 220 are positioned in the volume which is formed by the rotor-housing 225a and a bearing-housing 225b, and a bypass passage for the intake air opens in the rotor-housing 225a. The lower shaft 221 shown in FIG. 5 is a driven shaft of the mechanical supercharger, and extends through the rotor-housing 225a so as to project into the side-housing 226a.
Within the side-housing 226a is a wet type multiple plate clutch 230 which may be conventional and which transmits the rotation of a pulley 228 to the shaft 221. A shaft 229 of the pulley 228 is driven by a direct driving system of the internal combustion engine. The pulley 228 and the shaft 229 are rotationally supported in the side-housing 226a by ball bearing 233, together with a supporting plate 232 supporting multiple plates 231 of the driving side of the multiple plate clutch 230. To the shaft 221 is fixed a supporting plate 236 supporting multiple plates 235 of the driven side of the multiple plate clutch 230, and the multiple plates 235 are disposed between the multiple plates 231 of the driving side. The multiple plates 231, 235 rotate together with their respective supporting plates 232, 236 and are able to move axially thereon. The multiple plates 231, 235 are pressed into engagement for coupling the shafts 221 and 229 by the magnetic force resulting from excitation of coil 237 fixed to the side-housing 226a, and the force of this engagement is controlled by the amount of the excitation current supplied to the coil 237. Namely, the torque transmitted from the shaft 229 to the shaft 221 is controlled by the amount of excitation current supplied to the coil 237.
Oil is supplied between the multiple plates 231, 235 from a sump 238. The multiple plate clutch 230 has the property of permitting sliding between the multiple plates 231, 235 for small values of the current to the magnet 237. The oil operates as a lubricant and coolant and is stored in the sump 238 at the bottom of the side-housing 226a, and the lower parts of the supporting plates 232, 236 and multiple plates 231, 235 are submerged in the oil. Therefore the oil always exists between the multiple plates 231, 235.
An oil receiver 240 above the sliding-bearing 223 in FIG. 5 and a oil passage 241 from the oil receiver 240 to the sliding-bearings 223 are formed in the rotor-housing 225a so as to supply the oil to the sliding bearings 223 as a lubricant. The oil is supplied to the oil receiver by flying; that is, when the supporting plates 232, 236 rotate, the oil around the supporting plates 232, 236 is flung upward by centrifugal force and flows into the oil receiver 240. The oil supplied to the sliding-bearings 223 is also used for the lubrication of oil seals 242 fit to the outer faces of the shafts 221. The oil returns to the side-housing 226a through the passage 241c.
A pair of the shafts 221 project into the side-housing 226b as shown of the right side in FIG. 5, and meshing gears 245 are fixed to the ends of the shafts 221, as a result of which the two rotors 221 rotate simultaneously. In the bottom of the side-housing 226b is an oil sump 238' similar to that in the side-housing 226a. The lower part of the lower gear 245 is submerged in the oil within the sump 238'. The oil flung by the gear 245 lubricates the sliding bearings 223' and the oil seals 242'.
For the purpose of preventing a jolt in the thrust direction of the ball bearing 233, it has been proposed to use a double angular ball bearing, however the system has a mechanical loss and is noisy. The sliding bearings 223 and 223' in FIG. 5 support loads only in the radial direction. Additionally, the oil-supplied by flying is not always enough for the bearings 223 and 223'. Therefore it is possible that the bearings are damaged.